This invention relates to the manufacture of tinted glass.
The apparent colour of a light transmitting body depends on its spectral curve of transmission and this in turn is influenced by the particular light in which it is viewed. Accordingly, it is useful to refer to a particular standard light source. A standard has been established since 1931 by the Commission Internationale d'Eclairage (International Commission on Illumination) (CIE) which defines an illuminant C, nominally an average daylight source having a colour temperature of 6700 K., and a colour diagram on which can be plotted positions relating to the colour of an object viewed in that light.
It is well known that light of any colour can be matched by a suitable mixture of red, green and blue lights, and also that a mixture of two or more colours is matched by a corresponding mixture of their equivalent red, green and blue lights. Thus a units of colour A are matched by r units of Red, g units of Green and b units of Blue, or EQU a(A)=rR+gG+bB.
This equation is known as the tristimulus equation and r, g and b as the tristimulus values. C.I.E. have defined the particular red, green and blue colours of their system in such a way that the tristimulus values are always positive and the red and blue lights have zero luminous efficiency so that the luminance or brightness of a colour is directly proportional to the green tristimulus value. The reference stimuli defined in this way cannot in fact be achieved in practice, but they are convenient for mathematical analysis.
From the tristimulus equation, it follows that for one unit of colour A: ##EQU1## which may be rewritten as 1(A)=xR+yG+zB. The terms x, y, z are known as the colour co-ordinates of the colour A, and since their sum is unity, it follows that any colour may be uniquely represented by a pair of trichromatic co-ordinates x, y.
The C.I.E. have defined the colour co-ordinates for light of each wavelength within the visible spectrum and these may be represented diagrammatically on a graph having orthogonal x and y axes to give what is known as the C.I.E. colour diagram.